Ringing and signaling current supply for telephone system



RINGING AND SIGNALING CURRENT SUPPLY FOR TELEPHONE SYSTEM Filed July s,1953 A ril 3, 1956 J. K. MILLS EI'AL 4 Sheets-Sheet l J. K. MILLS B W 5R055 6.9 w

/N [/5 N TORS A 7'7'ORNEk April 3, 1956 J. K. MILLS ET AL 2,740,845

RINGING AND SIGNALING CURRENT SUPPLY FOR TELEPHONE SYSTEM Filed July 3,1953 4 Sheets-Sheet 2 J. A. MILLS lNl/Z/Il/TORS W5. R055 A TTORNEV FIG.2

Apr1l3, 1956 J. K. MILLS ETAL 2,740,845

RINGING AND SIGNALING CURRENT SUPPLY FOR TELEPHONE SYSTEM Filed July 3,1953 I 4 Sheets-Sheet 6 wvawrons M/LLS WS.ROSS I p7%pi A 7'7'ORNEV FIG.3

April 3, 1956 J. K. MILLS ET AL 2,740,845

RINGING AND SIGNALING CURRENT SUPPLY FOR TELEPHONE SYSTEM Filed July 5,1953 4 Sheets-Sheet 4 J. K. MILLS W 5 R055 lNVE N T OPS w wt ATTORNEYUnited States Patent RINGING AND SIGNALING CURRENT SUPPLY FOR TELEPHGNESYSTEM John K. Mills, Morristown, N. J., and Walter S. Ross, PortWashington, N. Y., assignors to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationJuly 3, 1953, Serial No. 365,898 6 Claims. (Cl. 17984) This inventionrelates to power supply systems and particularly to code ringingand tonesupply systems of the type used extensively in the telephone plant.

Supply systems of the type to Which this invention relates function inthe telephone plant to furnish ringing current at voltages required bytheparticular exchange sewed thereby; interrupted ringing current andground potential at proper intervals for funishing code signals formultiparty selective and/or semiselective ringing; interrupted groundpotential for signaling; and tone and other signal sources required bythe exchange. A system of this character is disclosed in United StatesPatent 2,694,- 106 of November 9, 1954, which resulted from a copendingapplication, Serial No. 216,957, filed March 22, 1951 by I. K. Mills,now Patent No. 2,694,106.

In such systems heretofore, and particularly in the sup ply systemdisclosed in the above-identified copending application, the power plantcomprises a ringing current generator, a tone generator, a regularinterrupter and a standby or spare interrupter as well as an auxiliarypower source. In the normal operation of such a plant the currentoutputs of the ringing and tone generators, which are of the staticconverter type, are fed directly, or by way of interrupter-controlledcontact springs in accordance with the signal codes required of theexchange, to the switch frame circuits at the exchange. In order toinsure a substantially continuous supply of the required ringing codesand tones, provision is made to permit the spare interrupter to besubstituted for the regular interrupter in the event of an emergencycondition involving the failure of the regular interrupter and also toautomatically transfer the load to the spare power source in the eventof failure of the regular commercial source on which the plant operates.

It is the object of this invention to increase the flexibility of and tootherwise improve code ringing and tone supply systems of the typedisclosed in the above-identified copending application.

In accordance with a particular feature of the supply system of thisinvention, spare ringing and tone current generators as Well as spareinterrupters are employed and circuit controls are provided foreffecting the substitution of the spare generator and interrupter units,separately, for the corresponding regular units in the event of failureof either of the latter.

More particularly, and in accordance with other features, the coderinging and tone supply system of this invention functions to furnishringing current at voltages required by the telephone exchange involved;to provide interrupted ringing current and ground at the properintervals for furnishing five code--ten party or eight partysemiselective ringing; to provide interrupted ground for signaling; toprovide the tones required by the particular exchange; to transferautomatically from commercial power supply to a battery-driven inverterin case of service power failure, with automatic transfer back when thecommercial power supply again becomes available; to transferautomatically to a spare interrupter in case of failure of the regularinterrupter; to transfer to spare ringing and tone generators in case offailure of the regular ringing or tone generators; to provide means oftransferring to the spare ringing and tone generators and the spareinterrupter and restoring to normal by dialing assigned numbers; toprovide means of transferring to the spare ringing and tone generatorsafter an automatic transfer of interrupters, or vice versa; and toprovide suitable alarm and guard signals.

The following description is made with reference to the accompanyingdrawings, in which:

Figs. 1, 2, 3 and 4 when combined in the manner shown in Fig. 6constitute a diagrammatic representation of the circuits and apparatusinvolved in the code ringing and tone supply system of this invention,and

Fig. 5 is a chart showing the closed and open intervals of the springpile-ups controlled by the interrupter cams during one completerevolution of the shaft thereof.

Referring to Figs. 1 and 3, the apparatus enclosed within the brokenline box designated INTI in Fig. 1 represents a motor-driveninterrupter, the shaft of which is re volved at the rate of onerevolution every six seconds by means of a motor M1 operating through areduction gearing indicated at 99. The slow speed shaft 100 ofinterrupter lNTl has fixedly mounted thereon a series of cams 1-11, eachof which controls an individual set of contact springs or springpile-ups. Similar equipment is contained in but not wholly illustratedin the broken line box INTZ of Fig. 3. This latter equipment constituteswhat hereinafter is referred to as the spare or secondary interrupterwhereas that shown in Fig. 1 is designated the regular or primaryinterrupter. Relay 23 shown in Fig. 1 controls a multiplicityof-armatures and their front and back contacts. These armatures serve toconnect the output conductors of interrupters INTI and INT2 to theswitch frame circuits X shown at the upper right of Fig. 1. It will beunderstood that the armature load, in practice, is distributed among agreater number of relays similar to relay 23, but the drawing is limitedto one such relay for the sake of simplicity of disclosure.

Fig. 2 discloses circuits and apparatus having to do particularly withthe manner in which the supply system is started functioning upon demandby the exchange equipment, and illustrates also a motor-driven inverterINV which is brought into service automatically, in the event of thefailure of the regular service supply, under control of a voltagecontrol circuit involving the vacuum tube 31. This control circuit, ofitself, constitutes no part of the present invention; it is disclosed inUnited States Patent 2,197,868, issued April 23, 1940 to C. S. Knowlton.Relays 2t), 21 and 22 represent those relays of a line finder, selectorand connector, respectively, which operate at various stages of atelephone connection to initiate the operation of the supply equipmentand to maintain it operating.

To the extreme right of Fig. 4 are shown schematically the ringingcurrent generator RG1 and the tone generator TGI of the regular supplyunit and the ringing current generator RG2 and the tone generator TG2 ofthe spare unit. These generators are static converters of any suitabledesign, the tone generators preferably being of the type disclosed inUnited States Patent 2,277,809, issued March 31, 1942 to L. R. Wrathall.Pig. 2 shows a relay 51 which is maintained operated, while shaft 106 ofthe primary interrupter INTI revolves, under control of the interruptercam Ill and condensers 55 (Fig. l), and 60 and which responds to thefailure of this interrupter to revolve to effect a transfer of the loadfrom interrupter INTI to interrupter INTZ. This feature constitutessubject-matter of the hereinbefore-identified J. K. Mills application.

The interrupters INTI and INT2 are identical and,

by way of illustration, are shown to include eleven spring Patented Apr.3, 1956 pile-ups and their associated cams 1-11, inclusive. It is to beunderstood that the cams and spring pile-ups may be fewer or greater innumber than eleven and may take forms other than those shown dependingupon the requlrements to be met at the telephone exchange.

Interrupter springs 1a function under control of the corresponding earn1 to apply ground potential at 57 (Fig. 1) to conductor 101 by way ofthe back contact and armature c1 of relay 23 and the upper make contactsof pileup 1a for a period of one and one half seconds for each completecycle of six seconds, and, during the same interval, to applysuperimposed battery 114 (Fig. 4) and ringing current from the output ofgenerator RG1 to conductor 102 by way of the armature d1 of relay 23 andits back contact, back contact and armature m1 of relay 23, conductors111 and 151, the No. armature and back contact of relay 150, through RG1to the battery 114. During the balance of the six second period, or forfour and one half seconds, battery 114 (Fig. 4) is connected toconductor 102 by way of conductor 115, armature 121 and the associatedback contact of relay 23, conductor 152, the No. 7 armature andassociated back contact of relay 150.

Interrupter springs 2a function under control of the associated cam 2 tosupply two spurts of ground potential from 57, each of one and one halfseconds duration spaced by an interval of one half second, to conductor103 by way of the back contact and armature e1 of relay 23 during eachcomplete cycle; during the same intervals superimposed battery 114 andringing current from generator RG1 are supplied to conductor 104 by wayof armature f1 of relay 23 and the associated back contact, back contactand armature m1 of relay 23, conductor 151, the No. 10 armature andassociated back contact of relay 150 to battery 114 by way of generatorRG1; during the remaining one half and two and one half secondsintervals of the cycle battery at 114 is connected to conductor 104 byway of armature 1 of relay 23 and the associated back contact, innermostcontacts of spring pile 2a, conductor 115, back contact and armature 711of relay 23, conductor 152, and the No. 7 armature of relay 150 and itsassociated back contact.

Interrupter cam 3 and its associated springs 3a cooperate to apply toconductor 105, by way of armature g1 and the associated back contact ofrelay 23 two spurts of ground potential. during each complete cycle, thefirst spurt being of a duration of one and one half seconds and spacedone half second from the second spurt which is of one half secondduration; during the remaining three and one half seconds conductor 105is held open.

Interrupter cam 4 and its associated springs 4a function to apply toconductor 106, by way of the back contact and armature 111 of relay 23,three spurts of ground potential during each complete cycle, one of oneand one half seconds duration and each of the two others of one halfsecond duration with a one half second interval between spurts; duringthe remaining two and one half seconds conductor 106 is held open.

Interrupter cam 5 and its associated contact springs 51: function toapply to conductor 107, by way of the back contact and armature 11,three spurts of ground potential, the first of one and one half secondsduration and spaced one half second from the second spurt which is ofone half second duration and, in turn, spaced one half second from thethird spurt which is of one and one half seconds duration; during theremaining one and one half seconds conductor 107 is held open.

Interrupter cam 6 and its associated contact springs 6:: function tosupply conductor 108, by way of the back contact and associated armature1'1 of relay 23, two spurts of ground potential each of one half secondduration and spaced by a time interval of two and one half seconds.

Certain of the functions of cam 7 and its associated spring pile-up 7aappear from the description of the operation of the system to be madehereinafter. It is apparent that the springs controlled by cam 7 areoperated for about one quarter second in each cycle. It is also apparentthat for one quarter second of the cycle ground at 57 is connected toconductor 109 by way of armature k1 and the associated back contact ofrelay 23, and for the remaining five and three quarters seconds of thecycle conductor 109 is connected to conductor 110 over armatures k1 andll of relay 23 and their respective back contacts.

Interrupter cam 8 and its contact springs 8a serve to apply to conductor120, superimposed battery 114 and ringing current from generator RG1 foran interval of one and one half seconds during each cycle, this circuitinvolving the back contact and No. 10 armature of relay 150, conductors151 and 111, armature m1 and the associated back contact of relay 23,middle contacts of spring pile-up 8a and the back contact and associatedarmature ql of relay 23; during the remaining four and one half secondsof the cycle conductor is connected to battery 114 by way of thelowermost contacts of spring pile-up 8a, conductor 115, back contact andarmature 111 of relay 23, conductor 152 and the No. 7 armature and backcontact of relay 150.

The interrupter springs 9a controlled by cam 9 operate and releasealternately six times during one complete cycle, each operation andrelease interval consuming one half second. During the intervals inwhich the springs are operated (illustrated) low tone is connected toconductor 121 in a circuit which includes armature 2'1 and theassociated back contact of relay 23, the outermost contacts of springpile-up 9a, back contact and armature s1 of relay 23, conductor 122, theNo. 11 armature and back contact of relay to the low tone terminal ofgenerator TGI; also during the same intervals ground at 57 is connectedto conductor 123 by way of the middle contacts of spring pile-up 9a,back contact and armature t1 of relay 23. During the alternate intervalsground at 57 is connected to conductor 124 by way of the innermostcontacts of spring pile-up 9a and the back contact and armature 111 ofrelay 23. Ground at 57 is also connected to conductor 121 by way of theupper transfer contact of spring pile-up 9a and the back contact andarmature r1 of relay 23.

Interrupter cam 10 interrupts its associated contact springs 10a at therate of 120 times a minute causing low tone from the source TG1 to beapplied at the same rate to conductor 125, the path from the tone sourceextending from the low tone terminal at TG1 over the back contact andarmature 11 of relay 150, conductor 122, armature s1 and the associatedback contact of relay 23, outermost contacts of spring pile-up 10a andthe back contact and armature v1 of relay 23; similarly, ground at 57 isapplied at the same rate to conductors 126 and 127 by way of theinterrupter spring contacts and the back contacts and armatures w1 andx1 of relay 23, it being apparent that when ground is being applied toone of the conductors 126 or 127 it is being disconnected from the otherconductor.

The interrupter cam 11 operates its spring pile-up at the rate of 120times per minute to alternately connect the condenser 55 to ground andto one terminal of the winding of relay 51 by way of the back contactand armature yl of relay 23 and conductor 123 for a purpose to be setforth in detail hereinafter.

Normal operation In normal operation and when no telephone calls are inprogress at the exchange, start relay 84 (Fig. 2) is held operated in acircuit extending from negative battery, through the winding of relay 84over conductor 13, back contact and inner left armature of relay 12, toground. Under this condition the ringing and tone current generators andthe interruptcrs are inactive. When ringing current, tones or groundpulses are required by the switching circuits at the telephone exchange,ground potential is connected to conductor 14 in a manner to bedescribed presently. It will be understood, for the purpose of thisdescription, that the ringing equipment illustrated is associated with aso-called community oflice or automatic exchange of the step-by-steptype and that the designations 20, 21 and 22, as hereinbefore indicated,represent well-known relays present in such an exchange which areoperated in response to the origination to a telephone call at asubscribers station and to subsequent steps incident to the completionof a telephone connection.

Upon the arrival of a call at the dial exchange the above referred torelay 20 in a line finder operates to start the finder searching for thecalling line as is well understood in the art. In operating, relay 20connects ground to the motor start conductor 14 which causes relay 12 tooperate over an obvious circuit. The ground potential on conductor 14 ismaintained by other relays 21 and 22 in the selector and connector,respectively, as the call progresses and is not removed until the calledsubscriber answers, or the call is abandoned.

Relay 12, operated, opens the operating circuit to relay 84 causing thisrelay to release its armatures. At its armatures and back contacts relay84 completes connections from the alternating-current service supply 15to the ringing current and tone generators RG1 and TGl,

by way of conductors 16 and 17, and to the regular interrupter INTI byway of conductors 18 and 19, it being observed at this time, that relay23 is assumed to be in .its unoperated condition as illustrated, so thatconductors 18 and 19 are extended to the motor M1 by Way of the.armatures a1 and b1 and their associated back contacts.

Relay 12 at its inner right armature and backcontact removes groundpotential from conductor 24 and at the associated front contact connectsground to conductor 25 for purposes to be described hereinafter.

Interrupter INTI functions under control of motor M1 and together withringing generator RG1 and tone generator TGI make available to theexchange circuits, by way of conductors X, machine ringing, tones andother code signals.

When ringing current, tones, etc., are no longer required, groundpotential is removed from conductor 14 causing relay 12 to release. Uponrestoring its armatures, relay 12 causes relay 84 to reoperate and todis connect the alternating-current source 15 from the ringing currentand tone generators RG1 and TGl and from motor M1 of the interrupterINTI.

Automatic transfer to inverter INV on power service failure TransformerSll, Fig. 2, tube 31, relay 32 and resistances and otentiometers 33, 34,35, 36, 37 and 37a and 38 form a circuit which is adjusted to causerelay 32 to release when the primary voltage at the transformer, that isthe voltage of the power source 15, is approximately 85 percent ofnormal value. Resistance 39 is provided to prevent release of relay 32during the open period of the contacts of the adjusting key 40 when thekey is being operated; Under normal power service voltage conditions,the voltage applied to the control gap of the tube 31 by potentiometer37 and resistance 36 is sufficient to cause this gap to fire on eachpositive half cycle. This causes the main gap of the tube to fire andfurnish current for the operation of relay 32. Relay 32, operated, holdsrelay 41 operated.

When the power service voltage falls below 85 percent of normal value,the control gap of tube 31 will not have sufiicient voltage across itand will cease to fire as will also the main gap, with the result thatrelay 32 will release, in turn. releasing relay 41.

Relay 41 at its outer right armature opens a short circuit acrossresistance 38 in the control gap potentiometer so that the tube 31 willfire again at a voltage at about 5 percent above the release voltagevalue. At

6 its outer left armature relay 41 completes an obvious energizingcircuit for relay 42 which relay thereupon operates and locks to groundby way of its own front contact and innermost left armature and theright front contact and associated armature of relay 43. Relay 43 isnormally held operated in a circuit to ground at the hack contact andoutermost left armature of relay 42.

Relay 42 at its outer right armature and back contact removes groundfrom the winding of relay 44, which relay,,however, remains operatedunder the control of the outer left armature and back contact of relay12. At its inner right armature and front contact relay 42 prepares anoperating circuit for relay 45 which is open at the front contact andouter left armature of relay 12 so that, whenever relay 12 operatesincident to the op eration of such telephone switching relays as 20, 21and 22, relay 45 will operate and start the inverter INV. The inverteris started by the connection of battery at the armature and frontcontact of relay 45 to the field and armature windings of thedirect-current motor M which motor drives the alternating-currentgenerator G in well-known manner.

The output leads 46 and 47 of generator G are connected to the two frontarmature contacts of relay 48, which relay remains released until relay44 restores its armature incident to the operation of relay 12 whichoccurs when such relays as 20, 21 and 22 operate to indicate the needfor ringing and/or tone currents by the telephone switching circuits.

When relay 1.2 does operate, relay 44 is released and causes thecompletion of the operating circuit for relay 43. With relay 12operated, relay 84 is released and the output leads 46 and 47 fromgenerator G are substituted for the power leads and 91 associated withthe power service supply 15 so that the alternatingcurrent load is nowtaken over by generator G.

Relay 44 is made slow releasing in order to delay the load transferuntil the inverter INV has attained full speed. Relay 42, operated,removes ground from the winding of relay 43, so that when the condenser50 has discharged, relay 43 will release. This condenser dischargedelays the release of relay 43 for about 15 seconds, so that when onceoperated, relay 42 will not release for this period of time even thoughrelays 32 and 41 have reoperated during this period. The purpose of thedelay is to prevent unnecessary transfers back to the main source 15during momentary restorals of service voltage after a service failure.

Manual start of inverter INV Ringing current or Zone generatortransfefwutomatic When there is no ground on the start lead 14, relay(Fig. 4) can not operate sincethe ground at through the thermistor 121is opened at the outer right armature and front contact of relay 12.When motor start ground is applied to the lead 14, relay 12 operates, aspreviously described, and connects ground to thermistor 121 but theoperation of relay 120 is delayed by the thermistor until relays 122,123 and 87 have operated because of the activation of the ringing andtone generators RG1 and TG1. The armature contacts of these relays areconnected in series from ground on the generator transfer key 132 toresistance 131 thus shunting down relay 124) and keeping it released.

Relays 122 and 123 are connected across the two output windings ofringing generator RG1 and relay 87 is connected across the alarm relaywinding of the tone If generator RG1 fails, either relay 122 or relay123 or both will release. If tone generator TG1 fails, relay 87 willrelease. The release of any of these three relays removes shuntingground from resistance 131 causing relay 120 to operate. Relay 120,operated, locks up to ground 130 by way of its own inner right armatureand front contact and the continuity contacts 129 of the relay 153. Atits right armature and front contact relay 120 completes an obviousoperating circuit for relay 153.

Relay 153, operated, transfers the locking ground for relay 120 to thegenerator transfer key 132 and at its No. 8 armature and front contactcompletes an obvious operating circuit for relay 150. Relay 150,operated, transfers the alternating-current input leads 16, 17 and theload conductors from the ringing current and tone generators RG1 and TG1to the corresponding generators RG2 and T62. Relay 153 also causes lamp149 to be lighted over an obvious circuit as a guard signal and may alsoinitiate the operation of a minor alarm signal. The contacts of relay122 and 123 will now be open since the output windings of the ringinggenerator RG1 are now devoid of current. However, relay 153 at its No. larmature and front contact connects ground over the armature contacts ofrelay 37, the No. 6 armature and front contact of relay 153, thearmature contact of relay 85, through resistance 133 to negativebattery. Thus relay 88 is shunted down. If ringing generator RG2 or tonegenerator TGZ fails after the transfer, relay S or relay 87 will releaseremoving the shunting ground from relay 88 and causing this relay tooperate. Relay 88, operated, causes lamp 139 to be lighted over anobvious circuit and initiates the operation of a major alarm signal byway of its outermost left armature and front contact and thermistor 98.Relay 88 locks by way of its own innermost armature and front contact.

To transfer back to generators RG1 and TGl after the trouble has beencleared, the generator restore key 138 is actuated to shunt down relay120 which thereupon releases and causes relay 153 to release. Therelease of relay 153, in turn, causes relay 150 to release to transferthe alternating-current source input leads 16, 17 and the load back togenerators RG1 and T61 and as relays 122 and 123 reoperate under controlof generator RG1, relay 120 remains shunted down when the generatorrestore key 138 is released.

Ringing current or tone generator transfer-manual To manually effect thetransfer of the load and the alternating-current leads 16, 17 fromgenerators RG1 and TGl to generators RG2 and T62, the generator transferkey 132 is operated causing shunting ground to be removed from thewinding of relay 120, which relay thereupon operates and causes relay153 to operate over an obvious circuit. Guard lamp 81 also lights in acircuit including conductor 96 and the No. 2 alternate contact of key132. Relay 153, operated, causes relay 150 to operate and to effect thetransfer as previously described. In this case, however, relay 153 locksup to the generator transfer key 132 and relay 121i releases as soon asrelay 153 operates and removes the holding ground.

To transfer back to generators RG1 and TGl, the generator transfer key132 is released causing relay 153 to be deenergized and to release relay150. Release of relay 150 transfers the alternating-current leads 16, 17and the load back from generators RG2 and TG2 to generators RG1 and TGl.

Interrupter transfer'automatic When there is no ground on conductor 14,interrupter INTI is not operating and ground at the inner right armatureand back contact of relay 12 is connected over conductor 24 to thewinding of relay 51, holding this relay operated. When relay 12 isoperated, the holding ground for relay 51 is removed but if theinterrupter is running, relay 51 is held operated in the followingmanner: When interrupter INTI is operating, the lowermost cam 11thereof, together with the other cams illustrated is driven by motor M1and being designed to interrupt the associated spring contacts at therate of 120 interruptions per minute, alternately connects condenser 55and the series resistance 56 (Fig. l) to ground at 57 and to the windingof relay 51 over conductors 58 and 59 by way of the back contacts andarmatures zl and y1 of relay 23 at the same rate. This periodicconnection of condenser 55 to the winding of relay 51 maintains relay 51operated while the condenser is charging, and the slow-releasingcharacteristic of the relay when in parallel with condenser 60 preventsit from releasing during the interval when condenser 55 is beingdischarged to ground at 57.

Should the motor M1, which is driving the interrupter INTI, fail, orshould the interrupter shaft cease to revolve for any reason, such as agear train failure, the 1PM spring pile-up controlled by cam 11 isarrested in either of two positions. If it stops when condenser 55 isconnected to the winding of relay 51, the relay will remain operateduntil the current falls below the value of the relay holding current. Ifthe interrupter stops with the conductor extending to the winding ofrelay 51 open, the relay will release after a short delay due to theparallel connected condenser 60.

Relay 51, released, completes an operating circuit for relay 62 whichmay be traced from negative battery, through the winding of relay 62,conductor 26, the front contact and outermost left armature of relay 61,conductor 27, outer left armature and back contact of relay 51,conductor 23, to ground at key 50. At its inner left armature and backcontact relay 51 connects ground to thermistor 63 and at its outer rightarmature and back contact completes an obvious energizing circuit forlamp 139.

Relay 62, operated, locks in a circuit extending from negative batterythrough the winding of relay 62, its front contact and innermost leftarmature, inner left armature and back contact of relay 67, frontcontact and left armature of relay 70, conductor 71, and the uppernormally closed contacts of key 50 to ground. At its middle leftarmature and front contact relay 62 causes relay 23 to operate over anobvious circuit. Relay 23 in operating transfers the load conductorsfrom interrupter INTI to interrupter INT2 by way of its upper armatures,and by way of its lower armatures a1 and b1 transfers the supplyconductors 18, 19 from motor M1 of interrupter lNT1 to the correspondingmotor of interrupter INT2. At its outermost left armature and frontcontact relay 62 establishes an obvious energizing circuit for lamp 72.

At its inner left armature and back contact relay 51, released, connectsground to the thermistor 63 and thence to conductor 95 by way of thefront contact and outermost right armature of relay 62. Conductor 95extends to the alarm circuit designated ALM but no alarm is brought inbecause of the delay induced by the ther mistor and the fact that relay51 reoperates from the interrupter INT2 over conductors 59' and 58which, like the corresponding leads 59 and 58 of interrupter lNTl extendto and are controlled by the spring pileup 11a associated with cam 11 ofinterrupter INTZ. The reoperation of relay 51 extinguishes lamp signal139 and also removes the ground from the thermistor 63. In case offailure of the spare interrupter INT2, relay 5]. will again release andremain released and ground will be connected over lead 95 to bring in amajor alarm.

With relay 23 operated, as described, all the conductors extending tointerrupter INTI will be disconnected from the switch frame circuits Xand the corresponding conductors extending to interrupter INTZsubstituted therefor. Also the power leads 18, 19 are transferred frommotor M1 of interrupter INTI to the motor of interrupter INT2 so thatthe spare interrupter will function upon operation of relay 12 and willtake over the load.

When interrupter INTI, which has failed, has been made ready for serviceagain, it is turned manually to the position in which cam 1 thereofoperates its associated springs and cam 8 does not operate its springs.This precaution is taken to prevent splitting ringing codes during amanual transfer.

To restore interrupter INTI to service the key 50 is held operated untilrelay 62 restores its armatures and extinguishes lamp 72. When key 50 isoperated it removes locking ground from relay 62 but a parallel groundis provided for holding the relay operated until a certain point in therotational cycle of the interrupter is reached. This parallel holdingcircuit may be traced from negative battery, through the winding ofrelay 62, its front contact and innermost left armature, inner leftarmature and back contact of relay 67, conductor 68, the motor holdcontact 66 of the spring pile-up controlled by cam 8 of interrupterINT2, conductor 97, to ground by way of the front contact and the No. 3armature of relay 61. When the interrupter INT2 reaches the end of itscode cycle, the motor hold contacts 66 open causing relay 62 to release.Relay 62, released, extinguishes lamp 72 and opens the leads to thealarm circuit ALM. It also releases relay 23 which functions, as is nowapparent, to transfer the load back to interrupter INTI, to open thecircuit to the motor of interrupter INT2 and to close the circuitthrough motor M1 of interrupter INTI.

Interrupter transfer-manual To manually transfer the load frominterrupter INTI to interrupter INT2, key 80 is operated to compete anobvious operating circuit for relay 67 which relay operates and locks byway of its innermost right armature and front contact over an obviouscircuit to ground at key 50. At its outermost right armature and frontcontact relay 6'7 completes a circuit for guard lampSI by way ofconductor 96 and, at its front contact and outer left armature, connectsground over conductor 83 to the lower movable spring on the motortransfer pile-up 7a of interrupter INTI. When the interrupter reachesthe end of its code cycle, the contacts controlled by the spring justmentioned close, connecting ground to the winding of relay 62. Relay 62operates.and locks toground at the inner left armature and front contactof relay 67. Relay 62 then effects the load transfer from interrupterINTI to interrupter INTZ and starts the interrupter INT2 in the mannerpreviously described. Transfer is effected at the end of the code cycleto prevent garbling of the codes.

To transfer back to interrupter INTI, key 50 is operated and heldoperated until relays 67 and 62 release and lamp 72 is extinguished.Holding ground is connected from interrupter INTZ to relay 67 until theend of the code cycle in the manner described in connection with theholding of relay 62 under Interrupter Transfer -Automatic. At that timerelay 67 releases causing relay 62 to release which starts interrupterINI and transfers the load thereto and stops interrupter INT2.

Dial transfer of ringing and tone generators and interrupters Dialtransfer is resorted to under emergency conditions, such as a failurecaused by an open lead or similar circumstance not detected by theautomatic transfer features.

The following description is directed to adial transfer when there hasbeen no preceding automatic transfer of generators or interrupters. Thiscondition assumes that the plant is running normally on ringing and tonegenerators RG1 and TGI and interrupter INTI and that some trouble hasoccurred that requires transfer in order to v10 keep the involvedexchange operating until the trouble can be located and cleared.

The number that has been assigned to ringing generator RG2 is dialedfrom any subset connected to the office, as from the station at whichthe dial D is located. Operation of dial D in accordance with thisnumber sets the switches, schematically indicated at 142, so that groundpotential is connected to conductor I43 and thence over the outer rightarmature and front contact of relay 70, front contact and the No. 6armature of relay 61, and winding of relay 144 to negative battery.Relay 144 operates in this circuit and locks over a circuit whichincludes its own No. l armature and front contact and the No. 6 armatureand front contact of relay 61. At its No. 3 armature and front contactrelay 144 completes an operating circuit for relay 153 which relayoperates and completes an obvious operating circuit for relay 150.

Relay 15G, operated, transfers the load conductors from ringing and tonegenerators RG1 and TGI to the corresponding generators RG2 and TG2.

At its No. 2 armature and front contact relay I44 connects ground by wayof conductor 26 to the winding of relay 62 and thence to negativebattery. Relay 62 operates in this circuit and completes an obviouscircuit to relay 23 which relay thereupon operates and transfers theload from interrupter INTI to interrupter INTZ. Relay 144 also lightslamp 145 over an obvious circuit.

Relay 62 at its outermost left armature and back contact removes groundfrom the winding of relay 70 as does also relay 153 at its continuitycontacts 149. Rellay- 70 releases and at its outer right armature andback, contact connects ground to conductor 143 to provide a busy signalif the number is redialed, and at its inner right armature and backcontact connects'the winding of relay 147 to conductor I46 extending tothe central ofiice switches 142.

When the trouble has been cleared, the number assigned to ringinggenerator RG1 is dialed whereupon ground is connected to lead 146extending to relay I47 causing this relay to operate. Relay I47,operated, causes relay 61 to release.

Relay 61, released, opens the locking circuit to relay Relay I44releases I44 causing this relay to release. relay 153 which, in turn,releases relay 150. Relay transfers the load conductors from generatorsRG2 to T62 to generators RG1 and TGl.

Relay 144, at its No. 2 armature and front contact, opens the circuit torelay 62. Relay 62, however, does not release at this time as it is heldoperated in a circuit which may be traced from negative battery throughthe winding of relay 62, its front contact and innermost left armature,inner left armature and back contact of relay 67, conductors 68,contacts 66 of interrupter INTZ, conductor 97, front contact and outerright armature of relay 51 to ground. This circuit is maintained untilthe end of the code cycle of interrupter INT2 and is then opened at 66,causing relay 62 to release and to restore its arms.- tures. When relay62 releases, it opens the operating circuit to relay 23 causing thisrelay to restore its armatures and thereby restore the load conductorsto interrupter INTI.

When ground is removed from conductor 146 at the switches 142, relay 147releases and operates relay 61 over an obvious circuit which includesthermistor 143. The thermistor delays the operation of relay 61 for ashort interval or" time. Relay 61 looks in a circuit independent of thethermistor 148. Relay 70 now operates in a circuit which may be tracedfrom negative battery,

through the winding of relay 70, the No. 4 armature and relay 144. Ifground has been removed from conductor 146 before relay 62 releases,relay 147 is held operated to ground over the middle right armature andfront contact of relay 62, conductor 155 and the No. 2 armature and backcontact of relay 61 and will not be released until relay 62 is releasedby the opening of contact 66 of interrupter INT2.

Dial transfer of interrupter after automatic transfer of ringing andtone generators It will now be assumed that the ringing and tonegenerators have undergone an automatic transfer and that it is desiredto dial transfer the interrupter. After the automatic transfer, the loadis being supplied by ringing and tone generators RG2 and TGZ by way ofinterrupter INTl. To effect the desired interrupter transfer the numberassigned to ringing generator RG2 is dialed at a remote station such asindicated by the dial D.

Operation of dial D in the manner indicated results in the applicationof ground potential to conductor 143 and the consequent operation ofrelay 144. The circuit functions in the manner previously described inconnection wtih a dial transfer with no preceding automatic transfer ofgenerators or interrupters except that in this case relays 12b and 153are locked operated due to the automatic transfer.

Relay 144, operated, locks up to its own No. 1 armsture and frontcontact through the back contact and No. 6 armature of relay 61 andcauses relay 62 to operate in a circuit extending from negative battery,through the winding of relay 62, conductor 26, to ground by way of thefront contact and the No. 2 armature of relay 144. It will be noted, asabove indicated, that relay 153 is already operated and locked so thatrelay 1 .4, in the present case, performs no function with respect torelay 153.

Relay 62, operated, causes relay 23 to operate and transfer the loadfrom interrupter INT 1 to interrupter INTZ. it also lights lamp 72.

With relays 62 and 153 operated, holding ground is removed from thewinding of relay 70 so that this relay releases and connects ground toconductor 143 to give a busy signal as the number is redialed. It alsocloses the path from lead 146 to the winding of relay 147.

"The load may be transferred back to interrupter lNTl by dialing thenumber assigned to ringing generator RG1 in the manner hereinbeforedescribed except that, in this case, the load remains on generators RG2and TGZ. The transfer of the load to generators RG1 and T61 can beeffected only by the operation or". the generator restore key 138 aspreviously described.

Dial transfer of ringing and tone generators after automatic zmnsfer ofinterrupter The automatic transfer of the load from interrupter lNTi tointerrupter INTZ has been described hereinbefore. This operation leftrelay 62 operated and locked to ground at the interrupter restore key 50by way of its own front contact and innermost left armature, the innerleft armature and back contact of relay 67, the front contact and leftarmature of relay '70 and conductor 71.

The number assigned to ringing generator RG2 is now dialed by means ofdial D causing ground to be applied to conductor 143 which, in turn,causes relay 144 to operate. Relay 144 causes relay 153 to operatewhich, in turn, operates relay 150. Relay transfers the load fromgenerators RG1 and TGI to generators RG2 and T62. Relay 144 at its No. 2armature and front contact connects ground to the winding of relay 62 byway of conductor 26 to hold relay 62 operated after relay 70 releasesand opens the holding circuit to relay 62.

The oad may be restored to generators RG1 and T61 by di pg the numberassigned thereto which connects ground to conductor 146 causing theoperation of relay 47. Relay 147 functions, as previously described, torelease relays 61 and 144, the latter releasing relay 153 12 which, inturn, releases relay to transfer the load back to generators RG1 andTG1.

Release of relay 144, however, does not release relay 62. The release ofrelay 144 removes the locking ground from relay 62 but if theinterrupter is not at the end of its code cycle, the motor hold contacts66 of interrupter INT2 furnishes a substitute locking circuit for relay62. If relay 144 released at the end of the code cycle when theinterrupter contacts 66 were open, relay 62 would release momentarilyand then reoperate on the subsequent release of relay 51 due to theprevious failure of interrupter INTl.

Should the dial D be operated following an automatic transfer of bothgenerator and interrupter units, the circuit functions as follows:Should the lead 146 be grounded as a result of the dial operation,nothing happens in. the circuit; should the lead 143 be grounded as aresult of the dial operation, interrupter INTZ will stop and the relayswill pump and a major alarm will be brought in. This condition clears upas soon as ground is removed from lead 143.

What is claimed is:

1. In a code ringing and tone current supply system for unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means responsive to a failure of the primary currentgenerator to supply at least a predetermined potential while conditionedto supply said load by way of one of said interrupters for atuomaticallytransferring said load to said secondary current generator, whereby saidload is supplied by said secondary current generator by way of the saidone of said interrupters, and means controlled from a remote point forsubstituting the other of said interrupters for the said one of saidinterrupters whereby said lead is supplied by said secondary currentgenerator by way of the other of said interrupters.

2. In a code ringing and tone current supply system for unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means responsive to a failure of the primary currentgenerator to supply at least a predetermined potential while conditionedto supply said load by way of said primary interrupter for automaticallytransferring said load to said secondary current generator, whereby saidload is supplied by said secondary current generator by way of the saidprimary interrupter, and means controlled from a remote point forsubstituting said secondary interrupter for said primary interrupter.

3. In a code ringing and tone current supply system for unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means responsive to a failure of the primary currentgenerator to supply at least a predetermined potential while conditionedto supply said load by way of said primary interrupter for automaticallytransferring said load to said secondary current generator, whereby saidload is supplied by said secondary current generator by way of saidprimary interrupter, and means responsive to a failure of said primaryinterrupter while functioning with said secondary current generator forsubstituting said secondary interrupter for said primary interrupterwhereby said load is supplied by said secondary current generator by wayof said secondary interrupter.

4. In a code ringing and tone current supply system for unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means responsive to a failure of either the primarycurrent generator to supply at least a predetermined potential or of theprimary interrupter while functioning to supply said load forautomatically substituting the corresponding secondary unit whereby saidload is supplied from said primary generator by way of said secondaryinterrupter in the event of failure of said primary interrupter or fromsaid secondary generator by way of said primary interrupter in the eventof failure of said primary generator, and dial controlled means forsubstituting either the secondary generator or interrupter for thecorresponding primary generator or interrupter not peviouslyautomatically substituted for.

5. In a code ringing and tone current supply system for t unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means responsive to a failure of the primary currentgenerator to supply at least a predetermined potential for automaticallysubstituting said secondary current generator therefor, dial controlledmeans for substituting said secondary interrupter for said primaryinterrupter, and means responsive to a failure of said primaryinterrupter before the operation of said dial controlled means forrendering said dial controlled means inetfective.

6. In a code ringing and tone current supply system for unattendedtelephone exchanges, primary and secondary current generators, anexchange load, primary and secondary interrupters for renderingavailable to said load the outputs of said generators in various codecombinations, means whereby said load is supplied from said primarycurrent generator by way of said primary interrupter, dial controlledmeans for substituting said secondary current generator and saidsecondary interrupter for said primary current generator and saidprimary interrupter respectively, and means whereby said dial controlledmeans functions when operated following a failure of either thesecondary generator or the secondary interrupter to substitute thereforthe corresponding primary element.

References Cited in the file of this patent UNITED STATES PATENTS2,225,907 Duguid et al Dec. 24, 1940 2,672,604 Mills et al Mar. 16, 1954

